1) Great. But why haven't you bought it yet? Saving it for something to look forward to, don't have the church yet, or is something holding you up from getting the quest (the Burns monster should be the final Halloween quest)?
2) Yup, like most graphic-heavy games, it'll drain your battery fast.
3) As the others said, you get the same amount of money from all buildings your friends helped with, but some buildings do help more than others in different ways. By spray-painting a building, they can clean it up and collect money from a building that otherwise wouldn't generate any money for them (school, Moe's, town hall, etc.). By tapping a friend's building that takes a long time to generate money (e.g. higher-level houses, prison, higher-level shops, etc.), the next round of their collections will be sped up a bit for that particular building.
4) Pretty sure, no. But some have taken multiple shots of their towns and merged them together in graphic manipulation programs (Gimp is a good free one, btw), and thus created an image of their whole towns. This takes a while though, and you need to be familiar with the program before attempting this, which will take even longer to learn. ;)